Those hole protectors are awful (IMO) mostly because those disturbs normal game play. It won't take many games when that paper-thin metal starts to form to same shape as wood beneath and edges rises from playfield and makes scoops harder to hit. In the other hand I think that those "inside scoop" protectors works fine, playfield is mostly protected from wear and those won't have affect on game play.

Example of good protector:
http://www.marcospecialties.com//images/products/HG-11/large.jpg

One big issue with these "over playfield protectors" is that those are often used just to cover wear. And for some reason it's marked as plus when selling game, I really don't understand how. I would always like to see actual condition of playfield when buying, especially with "premium" titles.

At home use I don't see much reason to put anything extra to games, keeping playfield clean and replacing balls occasionally does the trick.

Cliffys post sleeves are great, looking good and easy to clean. Other products I haven't tried so can't make any judgement...